The Ha-101-class submarine (波百一型潜水艦, Ha-hyaku-ichi-gata Sensuikan) was a transport submarine built for the Imperial Japanese Navy (IJN) during World War II. The IJN planned to build 12 boats, but only 10 vessels were completed by the end of the war. The IJN called these submarines Sen'yu-Shō type submarine (潜輸小型潜水艦, Sen-Yu-Ko-gata sensuikan). The type name, was shortened to Yusō Sensuikan Ko-gata (輸送潜水艦小型, Transport Submarine-Small Type).[2]
Several boats were converted to tankers or mother ships for the Kō-hyōteki model D "Kōryū" (甲標的丁型 蛟龍) midget submarines.
The Ha-101-class submarines were designed as small, cheap transport submarines to resupply isolated island garrisons. They displaced 436 metric tons (429 long tons) surfaced and 501 metric tons (493 long tons) submerged. The submarines were 44.5 meters (146 ft 0 in) long, had a beam of 6.1 meters (20 ft 0 in) and a draft of 4.04 meters (13 ft 3 in). They were designed to carry 60 metric tons (59 long tons) of cargo.[3]
For surface running, the boats were powered by a single 400-brake-horsepower (298 kW) diesel engine that drove one propeller shaft. When submerged the propeller was driven by a 140-horsepower (104 kW) electric motor. They could reach 10 knots (19 km/h; 12 mph) on the surface and 5 knots (9.3 km/h; 5.8 mph) underwater.[4] On the surface, the Ha-101s had a range of 3,000 nautical miles (5,600 km; 3,500 mi) at 10 knots (19 km/h; 12 mph); submerged, they had a range of 46 nmi (85 km; 53 mi) at 2.3 knots (4.3 km/h; 2.6 mph). The boats were armed a single mount for a 25 mm (1 in) Type 96 anti-aircraft gun.[5]
Project number S57. In February 1944, the IJN planned a small-size transport submarine, the IJA planned the Maru Yu.